Aeroseal Duct Sealing: How It Works, What It Fixes, and How It's Proven

What Aeroseal actually is

Aeroseal grew out of research at Lawrence Berkeley National Laboratory into a stubborn problem: duct systems leak most where access is worst. Instead of a person chasing leaks with a bucket of mastic, the sealant travels as a fine mist inside the pressurized ducts. Physics does the searching — air escaping through a gap carries sealant particles to that exact spot, where they snag on the edges and build up until the hole closes. It seals the small-to-moderate gaps and joints that riddle real duct systems, not gaping holes or disconnected runs.

The sealant itself is a water-based polymer that bonds at the leak points rather than coating the inside of your ducts — the same aerosol-sealing approach is used in homes, schools, and commercial buildings. Registers and the equipment are blocked off during the process, so the sealant goes only where escaping air goes: into the leaks.

The process, step by step

• Inspect and clean first: the sealant needs clean duct surfaces to bond to — on dusty ducts it bonds to the dust instead of the duct. Cleaning before sealing isn't an upsell; it's a requirement of the technology.
• Block and pressurize: supply registers are sealed off and the equipment is isolated, so pressure — and sealant — concentrates at the leaks.
• Baseline measurement: a computerized leakage test measures exactly how much air your ducts lose before anything is sealed.
• Injection: the aerosol sealant is introduced and monitored in real time — the technician watches the leakage number fall live as gaps close.
• Verification: you get the before-and-after report showing measured leakage reduction. The result is a number you can hold, not an adjective.

Why Phoenix ducts leak in the first place

Most homeowners focus entirely on the equipment while overlooking one of the most important components of the whole comfort system — the ductwork. Even a high-efficiency air conditioner can't deliver its full potential if conditioned air escapes before reaching occupied rooms. And Phoenix-area homes stack the deck: duct systems here typically run through extremely hot attics, ceiling cavities, garage ceilings, and other unconditioned spaces, where summer temperatures frequently exceed 140°F. Decades of that heat make duct mastic brittle and flex-duct jackets crack. Supply leaks dump air you paid to cool into the attic; return leaks pull hot, dusty attic air into the system — you pay to cool air that never arrives, then pay again as the system runs longer to compensate.

Duct leakage shows up as uneven room temperatures and hot-and-cold spots, reduced airflow, higher utility costs, longer HVAC run times, increased equipment wear, pressure imbalances, and dust infiltration — leaky returns are a major reason Phoenix homes fight dust, because every return-side gap is an unfiltered intake in the dirtiest air in the house.

That's why duct sealing shows up in every serious efficiency conversation here, and why it's the middle step of the clean-seal-insulate stack on our energy efficiency upgrades page: cleaning makes sealing possible, and sealing makes attic insulation honest — there's little point burying leaky ducts under fresh insulation.

Aeroseal vs. traditional duct sealing

Traditional duct sealing means a person manually accessing visible joints and applying tape or mastic. That works for exposed runs — but in a real house, many of the leaks sit behind drywall, beneath attic insulation, inside framing cavities, at concealed joints, and around connections no hands can reach. Aeroseal addresses those hidden leakage locations from inside the duct system itself, without demolition, which is why the two approaches are complements rather than competitors: accessible repairs get mastic, everything else gets the aerosol.

When Aeroseal is the right call — and when it isn't

Aeroseal shines when the duct runs are structurally sound but leaky: aged joints, dried-out connections, small gaps distributed through inaccessible runs. It is not a rescue for ducts that are crushed, collapsed, disconnected, or undersized — those need repair or replacement, and sealing them would be polishing a broken system. Radically undersized ducts are a design problem; sealing helps, but it can't create capacity that was never installed.

Homeowners typically end up considering Aeroseal from one of these starting points:

• Uneven temperatures or rooms that never cool properly — especially at the end of long attic runs
• Excessive dust despite good filtration (a classic return-leak signature)
• High utility bills, or comfort concerns that persist despite newer equipment
• Duct systems located in the attic, or simply older duct systems
• An HVAC replacement project — sealing first protects the new system's performance
• A broader home performance upgrade, where sealing is the middle step of the stack

What sealed ducts change day to day

When the leakage number comes down, the effects stack: improved airflow to the starved rooms, more consistent room-to-room temperatures, lower energy loss, reduced attic air infiltration, better overall system balance, and — in some homes — noticeably quieter airflow. It also supports indoor air quality, because the system stops pulling unfiltered attic air in through return-side gaps. The exact results depend on your duct system, its leakage level, and the overall HVAC design — which is precisely why every job starts and ends with a measurement instead of a promise.

Sorting all of this out is exactly what the free in-home duct inspection is for. Sometimes the honest answer is a few accessible mastic repairs; sometimes it's whole-system Aeroseal; sometimes it's replacement sized with a real Manual J load calculation. You get the measured leakage picture and the flat-rate quote in writing — and when it's close, both numbers.

What it costs — the one-paragraph version

Duct sealing is quoted flat-rate after the free inspection, and the before-and-after leakage test is part of every Aeroseal job. SRP's duct repair rebate currently covers 75% of the cost up to $400 for single-family detached homes in its territory (verified July 2026); APS has no active duct rebate. The full pricing breakdown, rebate details, and sealing-vs-replacement decision math live on the duct sealing cost guide — the canonical cost page, linked prominently below.